return function (str)

  local HexTable = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"}
  local A = 0x67452301
  local B = 0xefcdab89
  local C = 0x98badcfe
  local D = 0x10325476

  local S11 = 7
  local S12 = 12
  local S13 = 17
  local S14 = 22
  local S21 = 5
  local S22 = 9
  local S23 = 14
  local S24 = 20
  local S31 = 4
  local S32 = 11
  local S33 = 16
  local S34 = 23
  local S41 = 6
  local S42 = 10
  local S43 = 15
  local S44 = 21

  local function F(x,y,z)
    return (x & y) | ((~x) & z)
  end
  local function G(x,y,z)
    return (x & z) | (y & (~z))
  end
  local function H(x,y,z)
    return x ~ y ~ z
  end
  local function I(x,y,z)
    return y ~ (x | (~z))
  end
  local function FF(a,b,c,d,x,s,tip_text)
    a = a + F(b,c,d) + x + tip_text
    a = (((a & 0xffffffff) << s) | ((a & 0xffffffff) >> 32 - s)) + b
    return a & 0xffffffff
  end
  local function GG(a,b,c,d,x,s,tip_text)
    a = a + G(b,c,d) + x + tip_text
    a = (((a & 0xffffffff) << s) | ((a & 0xffffffff) >> 32 - s)) + b
    return a & 0xffffffff
  end
  local function HH(a,b,c,d,x,s,tip_text)
    a = a + H(b,c,d) + x + tip_text
    a = (((a & 0xffffffff) << s) | ((a & 0xffffffff) >> 32 - s)) + b
    return a & 0xffffffff
  end
  local function II(a,b,c,d,x,s,tip_text)
    a = a + I(b,c,d) + x + tip_text
    a = (((a & 0xffffffff) << s) | ((a & 0xffffffff) >> 32 - s)) + b
    return a & 0xffffffff
  end



  local function MD5StringFill(s)
    local len = s:len()
    local mod512 = len * 8 % 512
    --需要填充的字节数
    local fillSize = (448 - mod512) // 8
    if mod512 > 448 then
      fillSize = (960 - mod512) // 8
    end

    local rTab = {}

    --记录当前byte在4个字节的偏移
    local byteIndex = 1
    for i = 1,len do
      local index = (i - 1) // 4 + 1
      rTab[index] = rTab[index] or 0
      rTab[index] = rTab[index] | (s:byte(i) << (byteIndex - 1) * 8)
      byteIndex = byteIndex + 1
      if byteIndex == 5 then
        byteIndex = 1
      end
    end
    --先将最后一个字节组成4字节一组
    --表示0x80是否已插入
    local b0x80 = false
    local tLen = #rTab
    if byteIndex ~= 1 then
      rTab[tLen] = rTab[tLen] | 0x80 << (byteIndex - 1) * 8
      b0x80 = true
    end

    --将余下的字节补齐
    for i = 1,fillSize // 4 do
      if not b0x80 and i == 1 then
        rTab[tLen + i] = 0x80
       else
        rTab[tLen + i] = 0x0
      end
    end

    --后面加原始数据bit长度
    local bitLen = math.floor(len * 8)
    tLen = #rTab
    rTab[tLen + 1] = bitLen & 0xffffffff
    rTab[tLen + 2] = bitLen >> 32

    return rTab
  end

  --	Func:	计算MD5
  --	Param:	string
  --	Return:	string
  ---------------------------------------------

  function string.md5(s)
    --填充
    local fillTab = MD5StringFill(s)
    local result = {A,B,C,D}

    for i = 1,#fillTab // 16 do
      local a = result[1]
      local b = result[2]
      local c = result[3]
      local d = result[4]
      local offset = (i - 1) * 16 + 1
      --第一轮
      a = FF(a, b, c, d, fillTab[offset + 0], S11, 0xd76aa478)
      d = FF(d, a, b, c, fillTab[offset + 1], S12, 0xe8c7b756)
      c = FF(c, d, a, b, fillTab[offset + 2], S13, 0x242070db)
      b = FF(b, c, d, a, fillTab[offset + 3], S14, 0xc1bdceee)
      a = FF(a, b, c, d, fillTab[offset + 4], S11, 0xf57c0faf)
      d = FF(d, a, b, c, fillTab[offset + 5], S12, 0x4787c62a)
      c = FF(c, d, a, b, fillTab[offset + 6], S13, 0xa8304613)
      b = FF(b, c, d, a, fillTab[offset + 7], S14, 0xfd469501)
      a = FF(a, b, c, d, fillTab[offset + 8], S11, 0x698098d8)
      d = FF(d, a, b, c, fillTab[offset + 9], S12, 0x8b44f7af)
      c = FF(c, d, a, b, fillTab[offset + 10], S13, 0xffff5bb1)
      b = FF(b, c, d, a, fillTab[offset + 11], S14, 0x895cd7be)
      a = FF(a, b, c, d, fillTab[offset + 12], S11, 0x6b901122)
      d = FF(d, a, b, c, fillTab[offset + 13], S12, 0xfd987193)
      c = FF(c, d, a, b, fillTab[offset + 14], S13, 0xa679438e)
      b = FF(b, c, d, a, fillTab[offset + 15], S14, 0x49b40821)

      --第二轮
      a = GG(a, b, c, d, fillTab[offset + 1], S21, 0xf61e2562)
      d = GG(d, a, b, c, fillTab[offset + 6], S22, 0xc040b340)
      c = GG(c, d, a, b, fillTab[offset + 11], S23, 0x265e5a51)
      b = GG(b, c, d, a, fillTab[offset + 0], S24, 0xe9b6c7aa)
      a = GG(a, b, c, d, fillTab[offset + 5], S21, 0xd62f105d)
      d = GG(d, a, b, c, fillTab[offset + 10], S22, 0x2441453)
      c = GG(c, d, a, b, fillTab[offset + 15], S23, 0xd8a1e681)
      b = GG(b, c, d, a, fillTab[offset + 4], S24, 0xe7d3fbc8)
      a = GG(a, b, c, d, fillTab[offset + 9], S21, 0x21e1cde6)
      d = GG(d, a, b, c, fillTab[offset + 14], S22, 0xc33707d6)
      c = GG(c, d, a, b, fillTab[offset + 3], S23, 0xf4d50d87)
      b = GG(b, c, d, a, fillTab[offset + 8], S24, 0x455a14ed)
      a = GG(a, b, c, d, fillTab[offset + 13], S21, 0xa9e3e905)
      d = GG(d, a, b, c, fillTab[offset + 2], S22, 0xfcefa3f8)
      c = GG(c, d, a, b, fillTab[offset + 7], S23, 0x676f02d9)
      b = GG(b, c, d, a, fillTab[offset + 12], S24, 0x8d2a4c8a)

      --第三轮
      a = HH(a, b, c, d, fillTab[offset + 5], S31, 0xfffa3942)
      d = HH(d, a, b, c, fillTab[offset + 8], S32, 0x8771f681)
      c = HH(c, d, a, b, fillTab[offset + 11], S33, 0x6d9d6122)
      b = HH(b, c, d, a, fillTab[offset + 14], S34, 0xfde5380c)
      a = HH(a, b, c, d, fillTab[offset + 1], S31, 0xa4beea44)
      d = HH(d, a, b, c, fillTab[offset + 4], S32, 0x4bdecfa9)
      c = HH(c, d, a, b, fillTab[offset + 7], S33, 0xf6bb4b60)
      b = HH(b, c, d, a, fillTab[offset + 10], S34, 0xbebfbc70)
      a = HH(a, b, c, d, fillTab[offset + 13], S31, 0x289b7ec6)
      d = HH(d, a, b, c, fillTab[offset + 0], S32, 0xeaa127fa)
      c = HH(c, d, a, b, fillTab[offset + 3], S33, 0xd4ef3085)
      b = HH(b, c, d, a, fillTab[offset + 6], S34, 0x4881d05)
      a = HH(a, b, c, d, fillTab[offset + 9], S31, 0xd9d4d039)
      d = HH(d, a, b, c, fillTab[offset + 12], S32, 0xe6db99e5)
      c = HH(c, d, a, b, fillTab[offset + 15], S33, 0x1fa27cf8)
      b = HH(b, c, d, a, fillTab[offset + 2], S34, 0xc4ac5665)

      --第四轮
      a = II(a, b, c, d, fillTab[offset + 0], S41, 0xf4292244)
      d = II(d, a, b, c, fillTab[offset + 7], S42, 0x432aff97)
      c = II(c, d, a, b, fillTab[offset + 14], S43, 0xab9423a7)
      b = II(b, c, d, a, fillTab[offset + 5], S44, 0xfc93a039)
      a = II(a, b, c, d, fillTab[offset + 12], S41, 0x655b59c3)
      d = II(d, a, b, c, fillTab[offset + 3], S42, 0x8f0ccc92)
      c = II(c, d, a, b, fillTab[offset + 10], S43, 0xffeff47d)
      b = II(b, c, d, a, fillTab[offset + 1], S44, 0x85845dd1)
      a = II(a, b, c, d, fillTab[offset + 8], S41, 0x6fa87e4f)
      d = II(d, a, b, c, fillTab[offset + 15], S42, 0xfe2ce6e0)
      c = II(c, d, a, b, fillTab[offset + 6], S43, 0xa3014314)
      b = II(b, c, d, a, fillTab[offset + 13], S44, 0x4e0811a1)
      a = II(a, b, c, d, fillTab[offset + 4], S41, 0xf7537e82)
      d = II(d, a, b, c, fillTab[offset + 11], S42, 0xbd3af235)
      c = II(c, d, a, b, fillTab[offset + 2], S43, 0x2ad7d2bb)
      b = II(b, c, d, a, fillTab[offset + 9], S44, 0xeb86d391)

      --加入到之前计算的结果当中
      result[1] = result[1] + a
      result[2] = result[2] + b
      result[3] = result[3] + c
      result[4] = result[4] + d
      result[1] = result[1] & 0xffffffff
      result[2] = result[2] & 0xffffffff
      result[3] = result[3] & 0xffffffff
      result[4] = result[4] & 0xffffffff
    end

    --将Hash值转换成十六进制的字符串
    local retStr = ""
    for i = 1,4 do
      for _ = 1,4 do
        local temp = result[i] & 0x0F
        local str = HexTable[temp + 1]
        result[i] = result[i] >> 4
        temp = result[i] & 0x0F
        retStr = retStr .. HexTable[temp + 1] .. str
        result[i] = result[i] >> 4
      end
    end

    return retStr
  end

  return string.md5(str)

end